Exhaust gas turbochargers equipped with a waste gate, which are adjustable by an adjusting device or an actuating drive, are known from the related art. The actuating drive can be configured, for example, as a pneumatic actuating drive. However, as an alternative, the actuation or adjustment of the waste gate can also be achieved by an electric actuating drive. In contrast to the pneumatic actuating drives, the electric actuating drives can provide significantly higher actuating forces. Typically long term values of up to about 250 N are achieved, which are necessary to optimize the tightness of the waste gate in its closed position. If the electric actuating drive is a rotary actuator, then the force is often transferred via a four bar coupling mechanism or via a four bar drive. The four bar coupling mechanism has the driver arm, the output arm and the coupler, by which the driver arm is operatively connected to the output arm. The driver arm can be operatively connected directly to the drive or via the transmission. In this context the transmission includes the driving gear and the driven gear, which interact with each other in order to transfer a torque from the drive to the driver arm. The driving gear is assigned to the drive; and the driven gear is assigned to the driver arm.
The four bar coupling mechanism is usually configured in such a way that when the waste gate is in the closed position, the driver arm is in the range of an extended position. However, it is also possible to position the driver arm at a distance from the extended position in the closed position of the waste gate, in order to be able to compensate for wear and drift phenomena during continuous operation of the four bar coupling mechanism, the adjusting device and/or the waste gate. In this context, the term “extended position” is defined as the position of the driver arm, in which an imaginary straight line between a drive bearing point (at which the driver arm is operatively connected to the drive) and a connecting point between the driver arm and the coupler is essentially in alignment with the coupler or an imaginary straight line between the connecting points of the coupler with the driver arm and an output arm that is, represents quasi an extension thereof. The angle of rotation position range, in which the driver arm is located when the waste gate is in the closed position, can also be called the wear range, because this range is provided, as described above, to compensate for wear or drift phenomena.
The closer the position of the driver arm to the extended position in the closed position of the waste gate, the smaller is the torque that has to be generated for holding the closed position at the drive bearing point or that has to be applied by the drive onto the driver arm. However, inversely this also means that the adjusting force, which can be applied to the coupler by the driver arm, increases as the driver arm approaches the extended position. This means that the adjusting force, which can be generated at the coupler, in the wear range—as a result of approaching the extended position—exceeds an adjusting force that is permissible to act on the coupler and is intended for the device to be adjusted—for example, the exhaust gas turbocharger. This may result in the device being damaged.
The related art includes, for example, DE 10 2009 051 623.9, DE 10 2005 028 372 A1 and DE 102 45 193 A1. German patent document DE 10 2009 051 623.9 discusses an actuating device that is provided for a valve flap, including a four bar mechanism, which has a first pivot arm, which can be rotated directly or indirectly by an actuator and at the free end of which a transfer element is supported in a rotationally movable manner. The transfer element actuates a second pivot arm, which adjusts the valve flap and which is also connected in a rotationally movable manner to the transfer element by way of its free end. For this purpose, an elastic arrangement are provided that apply a tensioning force on the closed valve flap, which is placed at a stop in this position, when the four bar mechanism is in an extended position, in which a longitudinal axis of the first pivot arm runs substantially parallel to the transfer element.
In this case the elastic arrangement are configured as a spring cup or spring accumulator. The arrangements are connected between the two parts of a two part transfer element. German patent document DE 10 2005 028 372 A1 relates to an actuator that is provided for an actuating element; and this actuator comprises an electric actuating motor, an adjusting shaft adjusting the actuating element, and a transmission, which is arranged between the actuating motor and the actuating shaft and has a transmission input stage with a first gear wheel, which can be driven by an actuating motor, and a second gear wheel that meshes with the first gear wheel. Each of the two gear wheels should have at least two tooth systems that are arranged axially side by side with a tooth offset and have the same pitch circle diameters. Similarly it is provided that one of the tooth systems on the first gear wheel meshes with one of the tooth systems on the second gear wheel.
Finally, DE 102 45 193 A1 relates to an actuating unit having an actuator housing. The actuating unit comprises a speed transforming gear having a pair of wheels, where an actuating motor-side wheel has between its first engagement end and its a second engagement end a variable actuating motor-side rolling curve radius; and a throttle body-side wheel has between its first engagement end and its second engagement end a throttle body-side rolling curve radius that changes in a complementary manner relative to the actuating motor-side rolling curve radius.